java - 如何解决java中的流关闭错误？

Question

我真的很感谢所有阅读本文并尝试帮助我的人，以下是我尝试为大学套接字编程项目的服务器类编写的代码:

import java.io.*;
import java.net.*;
import java.io.File;

class Server{
    public static void main (String[]args)throws IOException{
        ServerSocket socket1 = new ServerSocket (8000);
        while (true) {
            Socket incoming = socket1.accept();
            new newclass(incoming).start();
        }
    }
}

class newclass extends Thread implements Runnable {

    Socket incoming;

    public newclass(Socket incoming) {
        this.incoming = incoming;
    }

    public void run() {
        try {
            byte x = 0;
            String z;
            String s = "HTTP 1.0 200 Document follows";
            String s1 = "Bad request message";
            BufferedReader input = new BufferedReader(new InputStreamReader(incoming.getInputStream()));
            PrintWriter output = new PrintWriter(incoming.getOutputStream(), true);
            DataOutputStream sending = new DataOutputStream(incoming.getOutputStream());
            File directory = new File("C:\\Documents and Settings\\Ahmed\\Desktop\\bla\\Server");
            File[] files = directory.listFiles();
            int x1 = files.length;
            if ((x1 - 3) < 10) {
                boolean done = false;
                while (!done) {
                    String line = input.readLine();
                    System.out.println(line);
                    if (line.equals("BYE")) {
                        output.println("BYE");
                        done = true;
                    } else {
                        if (line.trim().substring(0, 3).equals("GET ")) {
                            if (line.equals("<javalogo.png> HTTP    1.0")) {
                                File f = new File("javalogo.png");
                                int size = (int) f.length();
                                if (f.exists() == true) {
                                    output.println(s);
                                    output.println(size);
                                    output.println("javalogo1.png");
                                    DataInputStream bytefile = new DataInputStream(new BufferedInputStream(new FileInputStream(f)));
                                    while (bytefile.available() != 0) {
                                        x = bytefile.readByte();
                                        sending.write(x);
                                    }
                                } else {
                                    System.out.println("Getting file from main server");
                                    Socket socket2 = new Socket("127.0.0.1", 8100);
                                    BufferedReader bUsr = new BufferedReader(new InputStreamReader(System.in));
                                    PrintWriter pOut = new PrintWriter(socket2.getOutputStream(), true);
                                    BufferedReader bIn = new BufferedReader(new InputStreamReader(socket2.getInputStream()));
                                    pOut.println("GET <javalogo.png> HTTP 1.0");
                                    String rep = bIn.readLine();
                                    if (rep.equals("HTTP 1.0 200 Document follows")) {
                                        int len = Integer.parseInt(bIn.readLine());
                                        String fname = bIn.readLine();
                                        File f1 = new File(fname);
                                        f1.createNewFile();
                                        FileOutputStream fos = new FileOutputStream(f1);
                                        DataInputStream dis = new DataInputStream(socket2.getInputStream());
                                        for (int i = 0; i < len; i++) {
                                            fos.write(dis.read());
                                        }
                                        fos.close();
                                    } else if (rep.equals("File does not exist")) {
                                        output.println("Sorry, but the file was neither found in the proxy server or the main server or the name is wrong.");
                                    }

                                }
                            }
                            File f2 = new File("javalogo.png");
                            if (f2.exists() == true) {
                                int size = (int) f2.length();
                                output.println(s);
                                output.println(size);
                                output.println("javalogo.png");
                                DataInputStream bytefile = new DataInputStream(new BufferedInputStream(new FileInputStream(f2)));
                                while (bytefile.available() != 0) {
                                    x = bytefile.readByte();
                                    sending.write(x);
                                }
                            }
                        } else {
                            System.out.println(s1);
                            output.println(s1);
                        }
                    }
                }
                incoming.close();

            }
            output.println("Connecting to main server");
        } catch (Exception ex) {
            System.out.println(ex.getMessage());
        }
    }
}

现在我不明白为什么在运行以下客户端时会出现错误。
我收到这个非常奇怪的错误，缓冲读取器正确地从用户读取第一行，但在第二行时它给了我一个空异常，就好像客户端写了空或其他东西一样，我不明白。

无论如何，这是客户端代码，如果有人可以帮助我，我将非常感激。

import java.net.*;
import java.io.*;


public class Client {

    public static void main(String[] args) throws Exception {

        Socket socket1 = new Socket("127.0.0.1", 8000);

        BufferedReader bUsr = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter pOut = new PrintWriter(socket1.getOutputStream(), true);
        BufferedReader bIn = new BufferedReader(new InputStreamReader(socket1.getInputStream()));
        String cmd;
        String rep;
        while (true) {
            cmd = bUsr.readLine();
            pOut.println(cmd);

            System.out.println(rep = bIn.readLine());

            if (cmd.equals("BYE") || cmd.equals("END"))
                break;
            else if (rep.equals("HTTP 1.0 200 Document follows")) {
                int len = Integer.parseInt(bIn.readLine());
                String fname = bIn.readLine();
                File f = new File(fname);
                f.createNewFile();
                FileOutputStream fos = new FileOutputStream(f);
                DataInputStream dis = new DataInputStream(socket1.getInputStream());
                for (int i = 0; i < len; i++) {
                    fos.write(dis.read());
                }

                fos.close();
                System.out.println("Success");

            } else if (rep.equals("Connecting to main server")) {
                Socket socket1 = new Socket("127.0.0.1", 8100);
                BufferedReader bUsr = new BufferedReader(new InputStreamReader(System.in));
                PrintWriter pOut = new PrintWriter(socket1.getOutputStream(), true);
                BufferedReader bIn = new BufferedReader(new InputStreamReader(socket1.getInputStream()));
                String cmd;
                String rep;
                while (true) {
                    cmd = bUsr.readLine();
                    pOut.println(cmd);

                    System.out.println(rep = bIn.readLine());

                    if (cmd.equals("BYE") || cmd.equals("END"))
                        break;
                    else if (rep.equals("HTTP 1.0 200 Document follows")) {
                        int len = Integer.parseInt(bIn.readLine());
                        String fname = bIn.readLine();
                        File f = new File(fname);
                        f.createNewFile();
                        FileOutputStream fos = new FileOutputStream(f);
                        DataInputStream dis = new DataInputStream(socket1.getInputStream());
                        for (int i = 0; i < len; i++) {
                            fos.write(dis.read());
                        }

                        fos.close();
                        System.out.println("Success");
                    }
                }
            }

            bIn.close();
            pOut.close();
            socket1.close();
        }
    }

这是第一次在这个网站上询问任何问题，所以如果我做错了什么，我会非常乐意更改我所写的内容。

顺便说一下，服务器中“从主服务器获取文件”的部分是服务器本身成为主服务器的客户端的部分，从那里获取文件并将其发送到客户端，我没有添加主服务器代码，因为代码太多，但基本上它与服务器相同，没有 if 条件将其限制为目录中的 10 个文件。

Answer 1

一般来说，当出现 NullPointerException 时:

• 您尚未实例化您的对象
• 您的对象已被销毁(关闭)，因此不存在
• 您的 Actor 阵容无效
• 您的代码已覆盖您的对象指针

您需要检查堆栈转储以查看哪一个是正确的。

来自Jav Docs如果发生 I/O 错误并且 IOException 则读取可能会抛出 IOException可以给您指定的详细信息。稍后可以通过类 java.lang.Throwable 的 Throwable.getMessage() 方法检索错误消息字符串。

两点:

• IOException 详细信息为您提供了什么？
• 由于这是您的大学类(class)，请尝试向您的同学或助教寻求帮助